C# Language LINQ Queries Query collection by type / cast elements to type

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interface IFoo { }
class Foo : IFoo { }
class Bar : IFoo { }

var item0 = new Foo();
var item1 = new Foo();
var item2 = new Bar();
var item3 = new Bar();
var collection = new IFoo[] { item0, item1, item2, item3 };

Using OfType

var foos = collection.OfType<Foo>(); // result: IEnumerable<Foo> with item0 and item1
var bars = collection.OfType<Bar>(); // result: IEnumerable<Bar> item item2 and item3
var foosAndBars = collection.OfType<IFoo>(); // result: IEnumerable<IFoo> with all four items

Using Where

var foos = collection.Where(item => item is Foo); // result: IEnumerable<IFoo> with item0 and item1
var bars = collection.Where(item => item is Bar); // result: IEnumerable<IFoo> with item2 and item3

Using Cast

var bars = collection.Cast<Bar>();                // throws InvalidCastException on the 1st item
var foos = collection.Cast<Foo>();                // throws InvalidCastException on the 3rd item
var foosAndBars = collection.Cast<IFoo>();        // OK 

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